At least one person has been killed in protests across Libya on Thursday in what anti-government activists described as a "day of rage".
Amnesty International says a man was shot dead when security forces opened fire in the city of al-Bayda.
Police and protesters also clashed in Zentan and Benghazi, where one witness told the BBC at least 16 people are believed to have been killed.
This week's protests are the first in Libya, where dissent is rarely allowed.
Pro-government activists were also out on the streets in the capital, Tripoli. They shouted slogans in support of Libya's leader, Muammar Gaddafi.
The demonstrators in Green Square shouted: "We are defending Gaddafi and the revolution!" and "The revolution continues!" Others hurled insults at foreign media.
Pro-democracy protests have recently swept through several Arab nations, with the presidents of Tunisia and Egypt forced to resign amid growing unrest.
Gunfire in Benghazi
Amnesty International says protester Nacer Miftah Gout'ani was shot dead when security forces opened fire on demonstrators in al-Bayda. Dozens more were injured.
However, it said unconfirmed reports suggested as many as 12 people had been killed in the last two days.
Activists used social networking websites such as Facebook and Twitter to call for a "Day of Rage" on Thursday.
One witness, a woman in Benghazi who joined the protests on Thursday, told the BBC she saw hundreds of people taking part in the demonstrations.
She saw police firing their guns and she said they were not just firing into the air, but firing at people as well.
She said the word was that at least 16 people were killed in Benghazi alone.
However, it is impossible to confirm that figure independently.
A regional head of security was removed from his post in al-Bayda after the violence on Wednesday, local media reported.
In Zentan, a number of government buildings were set on fire, including a police station. A semi-independent local newspaper said five people had been arrested, two of them of Tunisian origin.
Wave of protests
Col Gaddafi is the Arab world's longest-serving leader, having ruled oil-rich Libya since a coup in 1969.
He has always insisted that the country is run by a series of people's committees, though most outside observers believe it is a police state with him firmly in control, the BBC's Jon Leyne reports.
The Middle East has recently seen a wave of protests fuelled by discontent over unemployment, rising living costs, corruption and autocratic leaderships.
This began with the overthrow of Tunisia's leader, Zine al-Abidine Ben Ali, in January. Last week, President Hosni Mubarak of Egypt resigned.
In recent days there have also been anti-government demonstrations in Yemen, Bahrain, and Iran.